Vortexing during draining through twin drain ports in a cylindrical tank

In this paper, the results of an investigation on the formation of vortex air core commonly known as `vortexing' occurring during draining of a liquid (water) column from a cylindrical tank through two eccentric ports (diameters d<sub>1</sub> and d<sub>2</sub>) simultaneously, are presented and discussed; d<sub>1</sub> is fixed whereas d<sub>2</sub> is varied. Before draining, the liquid column is induced with a rotation (N rpm) using a motorized stirrer where rotational speed can be controlled. Drain port eccentricities are equal (e). During draining, as the liquid level reaches certain height called `critical height' (Hc), a vortex air core develops and extends down touching the drain port. Results show that as N is increased, Hc is increased. At N=200rpm (highest speed tested), at the smallest eccentricity, lowest critical height occurs for the largest value of d₂ (equal to d₁). At larger eccentricities, a significantly different highly non-linear variation of Hc w.r.t N is seen with vortexing nearly suppressed for the case with drain port sizes equal. In many engineering systems, occurrence of `vortexing' is reported and hence, the present study carries significant practical relevance. All the studies reported so far were with single drain port and hence, the present study is first of its kind.